It is a common practice in the design of large computers, such as workstations and mainframes to provide redundant medium movers to cool the heat admitting electrical elements, such as CPU and memory modules. Such computers are provided with signals and/or alarms to warn in the event of a failure of the medium movers to avoid overheating of the electrical elements. However, because of the desire or need for the computers to operate without interruption for long periods of time on the failure of a medium mover, i.e. fan or blower provided to medium cool the electrical elements, the fan or blower works with one or more companion, i.e. additional units referred to as a redundant arrangement. This design, thus allows the computer to continue to operate uninterrupted in the event of the failure or inoperativeness of one of the fans or blowers of a cooperative group. Such systems are engineered to still provide adequate cooling even on the failure of one of the fans or blowers of a cooperative group. Hereinafter, the term fan is to be understood to refer also to a blower. Also the term medium is to be understood to include air, the preferred medium for workstations, servers and PC computers.
Past designs of such redundant systems, however, were not accomplished without a substantial down side. For one thing, past systems in order to provide necessary airflow required several relatively large plenums to provide for the required air and leakage distribution zones associated with the operation of the fans and to take care of reverse airflow created from failed fans. Other designs required the fans to be placed directly in front of the electrical elements.
There also was the problem of air pressure drop some systems inherently created by a failed fan which again was attempted to be solved by providing a relatively large strategically located plenum. This all required a significant enlargement of the enclosure or cabinet of the computer, and worked against the fundamental demand or interest in computer design for compactness.
As used herein the interest of compactness in terms of computer design has particular reference to allowing the employment of closeness of adjacent electrical elements, in shortening the electrical circuit distances between electrical interface systems and the accommodation of more electrical elements and interconnecting systems for a given enclosure space. Also interest in such compactness refers to the space required for the location and the number of fans needed in a given system and in the open spaces needed to assure efficiency of fan output in effectively conveying airflow to the electrical elements.
Past redundant systems also required the use in certain cases of more than a pair of cooperative fans and a particular reserved area for mounting the fans with the attendant need for more enclosure space. Without these design features the air cooling systems did not give the desired cooling efficiency and prevented or placed limitations on the number of electrical elements that could be cooled for a given cooling capacity of the redundant fan cooling system and enclosure size.
Even with these and the other noted design mandates certain redundant systems would not produce a constant bulk air mass flow on the occurrence of a fan failure and therefore suffered from not being able to utilize the cooling advantage of constant bulk air mass flow. This is because air in such systems is recirculated around the failed fan interfering or interrupting a constant bulk air mass flow.
One example of a prior redundant airmover system that addresses the reverse airflow and leakage problems noted above created by a failed airmover maybe found in U.S. Pat. No. 5,540,548 issued to A. N. Eberhardt et al. on Jul. 30, 1996, entitled "REDUNDANT BLOWER UNIT".